The present invention relates to a wafer polishing machine. More particularly, this invention is concerned with a wafer polishing machine adopting a chemomechanical polishing (CMP) process effective in flattening the surface of a wafer in the course of drawing IC patterns on the wafer.
Microscopic machining of ICs has been facilitated in recent years. IC patterns are drawn on many layers. It is therefore unavoidable that some irregularity occurs on the surfaces of the patterned layers. Conventionally, even when such irregularity occurs on one layer, a subsequent layer is patterned with the irregularity left intact. As the number of layers increases, the widths of lines or the diameters of holes diminish. This makes it hard to draw fine patterns. Defect can occur frequently. For this reason, after the surface of a patterned layer is polished to be flat, the next layer is patterned. Moreover, after holes are bored, a metallic layer for linking layers is formed by performing plating or the like. The metallic layer on the surface of the patterned layer is abraded so that the metallic layer will be left only in the holes. A wafer polishing machine (CMP machine) adopting the CMP process is used to polish wafers in the course of drawing IC patterns.
FIG. 1A and FIG. 1B are explanatory diagrams concerning machining to be performed according to the CMP process in the course of manufacturing ICs. FIG. 1A shows polishing of the surface of an interlayer dielectric to be performed so that the surface thereof will become flat. FIG. 1B shows abrasion of the surface thereof to be performed so that a metallic layer will be left in holes alone. As shown in FIG. 1A, after a pattern 2 is drawn on a substrate 1 by forming a metallic layer or the like thereon, when a dielectric interlayer 3 is formed, the pattern portion of the dielectric interlayer becomes higher than the other portion thereof. This results in an irregular surface. A CMP machine is then used to polish the surface. The surface is thus brought to the state shown in the right side of FIG. 1A. Thereafter, the next pattern is drawn. For forming a metallic layer linking layers, as shown in FIG. 1B, connection holes are bored in the lower layer having the pattern 2 drawn thereon, and a metallic layer 4 is formed by performing plating or the like. Thereafter, the CMP machine is used to fully abrade the superficial metallic layer 4.
FIG. 2 shows the basic structure of the CMP machine. As illustrated, the CMP machine has a polishing base 11 and a wafer holding head 21. An elastic polishing cloth 13 is bonded to the surface of the polishing base 11. The polishing base 11 rotates with an axis of rotation 12 as a center. Slurry that is an abrasive is supplied to the polishing cloth 4 on the rotating polishing base 1 through a nozzle that is not shown. The wafer holding head 21 holds a wafer 100 to be polished, presses the wafer against the polishing cloth 13 with a predetermined pressure, and rotates with the axis of rotation 22 as a center. The surface of the held wafer is thus polished. A groove is generally formed in the polishing cloth 13 in order to facilitate supply of slurry to the contact surface of the polishing cloth coming into contact with a wafer. In the drawing, the number of wafer holding heads 21 is one. In this case, the right side of the polishing base 1 is left unused, and production efficiency is unsatisfactory. Generally, a plurality of wafer holding heads 21, for example, two or four wafer holding heads 21 are included in order to concurrently polish a plurality of wafers.
When the CMP machine is used for polishing, the wafer 100 is first aligned and transported to a loader. The wafer holding head 21 holds the wafer placed on the loader using a suction mechanism, moves it to the polishing base 11, and presses it against the polishing base 11. The wafer is thus polished. When polishing is completed, the wafer holding head 21 holds the wafer using the suction mechanism and transports it to an unloader. Slurry that is an abrasive is adhering to the wafer 100 transported to the unloader. After the wafer is washed using a washer, it is dried. The wafer is then transported to a wafer collector such as a cassette. After the wafer is polished, IC patterns are drawn on the wafer according to a lithography method or the like. If abrasive particles or leavings were left intact, it would cause a defective IC pattern. Washing must therefore be carried out in order to make a wafer very clean. A washed wafer must be handled carefully for fear dust or the like may adhere to the wafer.
The CMP machine is required to meet such requirements that the performance in polishing must be high enough to ensure high-precision polishing, processing efficiency expressed as a throughput must be excellent, and an area needed for installation must be small. To meet the requirements, a plurality of polishing bases is included, and a wafer loading unit and a wafer unloading unit are used in common among the polishing bases. The wafer loading unit supplies wafers to the plurality of polishing bases. The wafer unloading unit transports wafers from the plurality of polishing bases. When this configuration is adopted, since one wafer loading unit and one wafer unloading unit are included relative to a plurality of polishing bases, the area needed for installation can be made smaller. Moreover, the time required for transporting wafers from the wafer loading unit to the polishing base or the time required for transporting wafers from the polishing base to the wafer unloading unit is shorter than the time required for polishing. Even when the above configuration is adopted, the processing efficiency will not deteriorate. Furthermore, polishing a wafer may be achieved by combining rough polishing and fine polishing. The rough polishing is performed at a high polishing speed but is insufficient in precision. The fine polishing is performed at a low polishing speed but ensures high precision. When the above configuration is adopted, one of the plurality of polishing bases may be used to perform close polishing, and the other polishing bases may be used to perform rough polishing.
The CMP machine having a plurality of polishing bases includes the wafer loading unit and wafer unloading unit. Nevertheless, the same transportation mechanism is used to transport wafers to the wafer loading unit and to transport wafers from the wafer unloading unit. Therefore, dust such as abrasive particles or leavings adheres to the transportation mechanism that has transported polished wafers. This kind of dust adheres to wafers that have not been polished and are transported to the wafer loading unit. The dust adhering to the polished surfaces of wafers does not pose a severe problem. However, the dust adhering to the backs of the wafers poses a problem in that a polishing pressure becomes inhomogeneous. This leads to deteriorated performance in polishing.
The present invention attempts to solve the above problems. An object of the present invention is to provide a CMP machine having a plurality of polishing bases, and a wafer loading unit and wafer unloading unit that are used in common among the plurality of polishing bases. The wafer loading unit supplies wafers to the plurality of polishing bases. The wafer unloading unit transports wafers from the plurality of polishing bases. In the CMP machine, the components are laid out so that adhesion of dust to unpolished wafers can be minimized.
To accomplish the above object, a CMP machine in accordance with the present invention has two polishing bases located mutually adjacently. Moreover, a wafer loading unit and wafer unloading unit are located mutually adjacently. A first polishing base and the wafer loading unit are located diagonally. A second polishing base and the wafer unloading unit are located diagonally. Transportation of a wafer to the wafer loading unit and transportation of a wafer from the wafer unloading unit are achieved using different systems.
To be more specific, a CMP machine in accordance with the present invention consists of first and second polishing bases, first and second wafer holding heads, a wafer loading unit, a wafer unloading unit, a first head rotating mechanism, a second head rotating mechanism, a first transportation mechanism, and a second transportation mechanism. The first and second polishing bases each have a polishing cloth attached to the surface thereof, and rotate the polishing cloth thereof. The first and second wafer holding heads each hold wafers and rotate while pressing the surfaces of the wafers against the polishing cloth. Unpolished wafers are placed on the wafer loading unit. Polished wafers are placed on the wafer loading unit. The first head rotating mechanism rotates the first wafer holding head so as to position it above the first polishing base, wafer loading unit, or wafer unloading unit. The second head rotating mechanism rotates the second wafer holding head so as to position it above the second polishing base, wafer loading unit, or wafer unloading unit. The first transportation mechanism transports an unpolished wafer to the wafer loading unit. The second transportation mechanism transports a polished wafer from the wafer unloading unit. The first and second polishing bases are located mutually adjacently. The wafer loading unit and wafer unloading unit are located mutually adjacently. The first polishing base and wafer loading unit are located diagonally. The second polishing base and wafer unloading unit are located diagonally.
According to the present invention, the first transportation mechanism and second transportation mechanism are included so that transportation of wafers to the wafer loading unit and transportation of wafers from the wafer unloading unit can be achieved using the different transportation mechanisms. Adhesion of dust to unpolished wafers can therefore be minimized.
The first and second wafer holding heads are designed to be able to rotate mutually independently while holding two respective wafers. The surfaces of the polishing bases can thus be used effectively.
One of the two polishing bases may be used for rough polishing, and the other polishing base may be used for fine polishing.
A mechanism for rotating the wafer loading unit and wafer unloading unit or moving them parallel to each other so as to shift them may conceivably be included. Using the mechanism, either the wafer loading unit or wafer unloading unit is selectively moved to a position at which wafers are received from or output to the wafer holding head. Consequently, the mechanism makes it possible to switch the wafer loading unit and wafer unloading unit, and to receive or output wafers at the same position. When the mechanism is utilized, three polishing bases may be included and assigned to rough polishing and fine polishing. Two polishing bases are assigned to polishing requiring a long processing time. This may lead to an improved throughput. However, according to this configuration, the first and second transportation mechanisms must access the common position, at which wafers are received from or output to the wafer loading unit or wafer unloading unit, from different directions. A component for aligning unpolished wafers and a component for washing polished wafers must be located in different directions. This leads to an increase in the area required for installing the CMP machine. In particular, a bay through which wafers are moved in or out of the CMP machine must be widened. This is not preferable in constructing an automated manufacturing process.